Mad Observations: Many organisms (ranging from apples to mammals) use chemicals called pheromones to communicate. As you'll see if you follow that link to Wikipedia, these signals are used to communicate many different things, from "follow me" to "look out!" The "look out!" class, better known as alarm signals, had been well-established in mammals. And humans are mammals...
Mad Reference: Mujica-Parodi LR, Strey HH, Frederick B, Savoy R, Cox D, et al. (2009) "Chemosensory Cues to Conspecific Emotional Stress Activate Amygdala in
Humans." PLoS ONE 4(7): e6415. doi:10.1371/journal.pone.0006415 (full text available online)
Mad Hypothesis: Humans, like other animals, have alarm pheremones. Those pheremones invoke an alarm response in humans (for example, the known responses associated with fear). In other words, humans produce something that makes other humans scared when they smell it (or at least makes other humans behave in ways that scared humans behave).
Mad Experiment: The researchers collected sweat from two groups: first-time tandem skydivers (the experimental group), and people exercising (the control group). They then had people smell this sweat to see if they could tell the difference (ie, they asked people which sample smelled worse), to rule out a noticeable difference in smells (the subjects couldn't tell the difference). They then had subjects breathe in this sweat (one sample or the other) while undergoing an fMRI (the test where they look at what part of your brain lights up in response to different stimuli). They also had the subjects identify whether faces looked frightened or not (we'll get into why they did that below).
They All Laughed, But: Actually, it turns out nobody was laughing. The most interesting thing I learned by reading this paper is that there had already been six studies published about a human alarm substance transmitted via sweat. In two, subjects were able to identify whether the sweat came from someone watching a scary movie or a "benign" film. Another study found that subjects were better able to complete a word-association task when they smelled scary-movie sweat (again vs "benign film" sweat). The remaining three found that stress sweat caused subjects to interpret expressions as more fearful, to be less likely to judge a face as positive, and to be more likely to be startled by "auditory stimuli" (that last one, which I like to think of as the "boo!" study, makes me laugh somewhat maniacally). If you're interested, all of those references are in the paper (linked above); I don't want to repeat them all here.
However, this new study did find two new things:
- The previous studies had used scary movies or preparation for difficult exams to provoke the stress in the experimental groups. By using first-time skydivers, this one provides us a different variety of stress, broadening the range of where we can expect to find this signal.
- The previous studies had looked at whether subjects could identify sweat from stressed people, or what subjects' psychological responses were to the fear sweat. This study showed a physical response to the fear sweat, specifically activation of the amygdala (the part of the brain associated with emotion), just as expected.
This new study also threw in an "is this face scared?" test, but that was just to confirm that those results agreed with the previous results (they did).
Mad Engineering Applications: This area of research positively screams to be implemented by mad engineers. You might not be able to make a fear gun, per se, but it just might be possible to make a fear bomb. And, combined with other research (including a piece in an upcoming Mad Science Monday), a good mad engineer could even use this to make his or her henchmen more effective (I mean, sure, your henchmen should already be afraid of you, but with this you could make sure they're working scared even when you aren't around). There simply have to be at least a few DARPA projects associated with this.
Do you have any other ideas for how to apply this? Let me know in the comments.